Desalination of ocean water

ABSTRACT

An improved distillation of water. involves distilling significant quantities of water at temperatures well below the boiling point. During distillation, a compound is taken from a liquid-phase to a gas-phase and then condensed to the liquid-phase again to get a pure liquid. The present invention uses water sprayed ( 105 ) and absorbed onto a solid surface such as micro-powder ( 104 ) made from wood as a starting material. Absorbing water onto such a surface results in rapid evaporation with a relatively low temperature gradient when the water and particles are agitated. The present invention could be characterized as solid-phase distillation.

BACKGROUND OF THE INVENTION

1. Area of the Art

The present application concerns desalination of ocean water andspecifically a new method to get pure water easily.

2. Description of the Prior Art

The world faces serious water problems. The increased warming of theocean surface brought on by increases in atmospheric carbon dioxide andother “greenhouse gases” is a big problem for island countries.Increasing temperatures cause the oceans to rise as polar ice caps melt.This may drown the islands. Meanwhile, elevated water temperaturesdamage the coral reefs so that island dwellers also face a shortage offood. At the same time increases of atmospheric temperature promotedesertification. Desert dwellers lack water for direct consumption andfor agriculture. Desert dwellers also face a food shortage. Both ofthese problems are environmental. All living things contain water as amajor constituent of their bodies. Most biological functions and manybiological structures depend on water and are not possible under a dryor dehydrated state. “Dry” means “death” for most living creatures.

Therefore, the problem of water shortage is very important for allhumans. By the middle of the twenty second century it is estimated thatworld population will exceed 10 billion. This rapid increase in theworld's population will increase the already intense competition forwater, food and energy. These problems are closely related to each otherand are not readily separable.

Most water on Earth is ocean water (seawater). Pure water exists in ice(glaciers and snow), rain, rivers, ponds, lakes, and undergroundaquifers. The agriculture use of water depends on the above-mentionedwater sources. Unfortunately, many aquifers contain water rich inminerals that accumulate in the soil following prolonged irrigation.This accumulation causes the so-called “salt injury” to plants. Wherethe water is high in sodium, the actual structure of the soil is damagedas sodium replaces calcium in clay minerals.

The 97.5% of the planet's water is ocean water, which cannot be usedagriculturally without the removal of salt—desalination. There arebasically two popular desalination processes: distillation and membraneseparation. Distillation is a process in which water molecules evaporatefrom seawater and are subsequently condensed as pure water. The membraneseparation process involves either “electron dialysis” (the ED method)or “Reverse Osmosis” (the RO method).

Distillation yields pure water and the residue from this process issalt. The membrane processes ED and RO trap ions and salts so theresidue is pure water. Distillation requires much energy for heating thewater to accelerate evaporation whereas and the membrane processesrequire expensive membranes.

The practical problem of the desalination of ocean water is one ofperformance at an industrial level since such huge amounts of water areneeded for agriculture on a scale that can convert the deserts intogreen plantations. Photosynthesis is the only significant process bywhich living organisms capture solar energy and store it by synthesizingglucose from carbon dioxide and water. It is a well-known rule of thumbthat the growth of agricultural crops requires a weight of water aboutone thousand times the weight of the harvested crop.

Standard ocean water contains about 3.4 weight % of salts with a pH of8. The most prevalent anions are the chloride ion (19,000 mg/l) and thesulfate ion (2,600 mg/l). The common cations are the sodium ion (10,650mg/l), the magnesium ion (1,300 mg/l), the calcium ion (400 mg/l) andthe potassium ion (380 mg./l.) There are also lower levels of thebromide ion, the carbonate ion, the boron ion and the strontium ion. Inaddition there are traces of iron, silica, and calcium carbonate.

Each of these ions has a diameter of several Angstroms (10⁻¹⁰ m). Thehydrated ions are in the same dimensional order of magnitude. Theseparation efficiency of the membrane desalination processed is owed tothe ion trapping ability and the ion permeability of the membranes. Theaffinity and the pore sizes of the membranes are key to the separationresults. The manufacture of the membranes must be carefully done andspecial polymers are required. For the ED method ion-exchange polymersare favored whereas for the RO method cellulose acetate and similarneutral polymers are preferred. Modification of the polymer matrix, forexample by cross-linkage and side-chain modification, has been tried toimprove efficiency. Nevertheless, it is still difficult to remove allions.

On the other hand, the distillation method is a standard laboratorymethod for separation of a liquid from various contaminants. After theremoval of particulate matter, ocean water is boiled and evaporated. Theresulting steam is then cooled to condense it into liquid water. Thecommon fractional distillation tower is able to yield a large amount ofpure water. The problem is to use energy efficiently. A number oftechnologies attempt to decrease the total number of calories needed todistill pure water from ocean water.

For producing drinking water it is necessary to remove essentially allions, because our body already contains a critical balance of most ofthe ions found in ocean water and can be damaged by additional ions. Foruse in agriculture it is also necessary to remove essentially all ions.As mentioned above, the accumulation of salts in agricultural landsrenders the soil non-arable so that the farmer must give up cultivationof the affected land. In the world there are many regions where this hasalready occurred. There are a myriad of problems resulting from shortageof water—formation of deserts, salt injury to agriculture, as well aslack of drinking water. These problems necessitate complex systems forthe long-distance transport of water as well as “water wars” when wateris taken from one region to benefit another.

SUMMARY OF THE INVENTION

The present invention is a new process for desalinating ocean waterthrough evaporation to yield pure salt-free water. Essentially, theprocess consists of the evaporation of water from the surface of a solidsurface while applying energy as heat and/or stirring. The ocean waterpre-heated by the sun and/or other energy sources is introduced into acontainer and sprayed onto the surface of a fine particulate materialthat has large surface area. Interaction of the water molecules with thesurface accelerates evaporation. This allows significant evaporationwith a lower energy input than conventional distillation. Followingevaporation the water vapor is condensed to yield pure water. Theresulting water is acceptable for agricultural use as well as fordrinking.

DESCRIPTION OF THE FIGURES

FIG. 1 is diagrammatic representation of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description is provided to enable any person skilled inthe art to make and use the invention and sets forth the best modescontemplated by the inventor of carrying out his invention. Variousmodifications, however, will remain readily apparent to those skilled inthe art, since the general principles of the present invention have beendefined herein specifically to provide a process that enhancesevaporation from ocean water by combining the ocean water with aparticulate material.

In nature water circulates through the environment in three physicalstates—solid, liquid, and gas. Water evaporates from land or from thesurface of bodies of water in response to warming by the sun. Theresulting water vapor circulates through the atmosphere and collects asclouds. Upon sufficient cooling the water condenses from the clouds andfalls as rain or snow. The evaporation from land or water surface is notdependent on a great gradient in temperature. Rather the large scale ofthe surfaces involved make it possible for a modest rise in surfacetemperature to result in the distillation of massive amounts of purewater from the Earth's surface. The present inventor has realized thatby greatly multiplying the evaporative surface it is possible to greatlyenhance the rate of evaporation of water. In thinking of evaporationfrom the huge surface area of the oceans one can consider theevaporative area as being two-dimensional. The two-dimensional area isin reality a three-dimensional area. The whole surface area of the Earth(509,949,000 km²) can be essentially converted to the surface area of aplurality of small particles by the following equations.

Here S=the surface area, V=the volume, W=the weight, D=the density andR=the radius of the Earth. Similarly, s=the surface area, v=the volume,w=the weight, d=the density and r=the radius of an aggregate pluralityof small particles (micro-powder) that are used to substitute for theEarth's surface.S=4πR ²  (1)s=4πr ²  (2)Allowing S to equal the total sum of the surface areas (s) of aplurality (n) of particles (S=nχs)

$\begin{matrix}{n = {\frac{S}{s} = \left( \frac{R}{r} \right)^{2}}} & (3)\end{matrix}$V=4/3πR ³  (4)v=4/3πr ³  (5)

$\begin{matrix}{\frac{V}{v} = \left( \frac{R}{r} \right)^{3}} & (6)\end{matrix}$W=4/3πR ³ ·D  (7)w=4/3πr ³ ·d  (8)Taking n from (3) we derive

$\begin{matrix}{{n \cdot W} = {{\left( \frac{R}{r} \right)^{2} \times \frac{4}{3}\pi\; r^{3} \times d} = {\frac{4}{3}\pi \times R^{2} \times d}}} & (9)\end{matrix}$The Earth's radius R=6.37×10⁶ m. Therefore:nW=8.5×10¹⁶ ×r kg [r: [m]]  (10)

If the density D of the Earth is 5.5 g/cm³, the weight W is about5.97×10²⁴ metric tons using equation (7). However, using equations (9)and (10) it is possible to calculate the weight of micro-powder that hasa combined surface area equal to that of the Earth. Assuming that themicro-powder is cellulose with a density of 0.5 g/cm³, one can calculatethat for micro-particles having a radius r of 1 cm, the weight ofmicro-powder having the surface area of the Earth is about 8.5×10¹¹metric tons. When r is reduced to the micrometer range (1×10⁻⁶ m), theweight becomes 8.5×10⁷ metric tons.

This gives an indication of how tremendous is the surface area of smallparticles. By using small particles it is possible to essentiallyduplicate the entire evaporative surface area of the Earth with a“relatively

A preferred material is fine cellulosic powder produced by exhaustivedisruption of wood cellulose. Saw dust and similar cellulosic wastematerials can be mechanically disrupted by a process of continuedgrinding and stirring to provide such a material.

As will be explained below, interaction of the water molecules with theparticle surface provides another significant improvement in efficiency.A weight of micro-powder that is orders of magnitude below the figurecalculated above is actually capable of duplicating the evaporativecapacity of the entire Earth. This makes it possible to make arelatively small but very efficient evaporative system usingmicro-powder.

Free-Water

In understanding the additional efficiencies provided by micro-powder,it is first necessary to consider the state of water. Water is, perhaps,the most basic compound in chemistry. The structure of water makes itideal for a type of intramolecular interaction popularly known as“hydrogen bonding”. Because of this interaction liquid water exists in aquasi-polymeric state where individual water molecules are linked toform a “cluster”. The specific heat, boiling point, freezing point andrelated physical properties of water show very different values whencompared to similarly sized molecules that do not exhibit hydrogenbonding. The boiling point of 100° C. is often used for illustration ofthe hydrogen bond phenomenon. Water vapor, the gaseous stage of water,exists as mono- or di-water molecules. The heat required forvaporization of liquid water represents the overall energy required tomove the molecules from polymeric “cluster” state to the vapor statewherein clusters are replaced by water monomers or dimers. The specificheat of water is 4.3 j/g·K under standard conditions. The normalisotropic bulk water is called “free water”. This means water-watermolecular interactions are the same in all directions. If a hydrophiliccompound is introduced into the system, the water-water interactionschange slightly. The effect of added ions is an example of this effect.An ion dissolved in the water becomes hydrated; this means that anadditional interaction is added—namely the ion-water interaction. Thisinteraction is not large, so the specific heat of seawater is reducedonly to 3.9 J/g·K. However, it is important to note that another forceis able to change water-water interaction. The ion-water interaction isweak, and relaxation time for the interaction is short. The interactionof a water molecule with an ion not affected by other water molecules,so it becomes easier to heat to the water molecule. Bound water isanother state of water in which the water-water interactions aredisrupted. A completely hydrated molecule contains immobilized water orassociated tightly bound water. Water interactions can also be disruptedby hydrophobic materials. Strongly hydrophobic particles such as thoseof poly-teterafluoroethylene can also be effective in the presentinvention. At the present time IR, Raman, or Nuclear Magnetic ResonanceSpectrometry can distinguish these various states of waterexperimentally.

The interaction of water-water and water-other molecule shows that it ispossible to alter the heat transfer characteristics of the watermolecule. Weakening the water-water interactions can lower the amount ofenergy needed to convert water from a liquid to a gas. The surface of asmall particle is optimal for producing interactions that change theamount of energy needed to evaporate water. That is, the energy neededto evaporate a water molecule can be reduced by the reducing thewater-water interaction.

The most effective materials for this purpose appear to be hydrophiliccompounds such as natural polysaccharide macromolecules found in plantmaterials such as wood, paper, bamboo, and rice straw as well asproteins and inorganic metal oxides such as silica (silicon dioxide),alumina (aluminum oxide). titania (titanium dioxide), magnesia(magnesium oxide), iron oxide, other metal oxides, clays, etc.

The source of energy for the evaporative process is not critical. Energycan be supplied as normal convective or conductive heating, or radiativeheating by visible, infrared, or microwave radiation or simply bysunshine. Another method is a mechanical heating through friction (e.g.,by stirring).

Free water exhibits strong water-water interaction and much energy isneeded to overcome the interaction and convert liquid water to thevapor. To weaken the interaction water-water is an important way ofreducing the amount of energy needed to evaporate water.

Vapor Removal

There is a normal vapor-liquid equilibrium between water vapor andliquid water. This characteristic of the invention is concerned with thepromotion of a non-equilibrium condition. The evaporation of ocean wateris controlled by the vapor-liquid equilibrium under constant temperatureand pressure conditions. Reducing the pressure is another way to promotean increase in the rate of evaporation. In a closed system vaporpressure of water p₁ and atmospheric pressure p₂ combine to yield theequilibrium pressure p. The vessel volume affects this pressure at agiven temperature because the vessel's volume controls the total vaporvolume in such a closed system. If the water vapor is allowed to flowinto a condenser to be converted into liquid water, the vapor pressureof water p₁ is reduced in the system and evaporation is promoted. A fancan be provided in an evaporation system to promote circulation of thewater vapor into the condenser.

FIRST EXAMPLE

FIG. 1 shows a diagrammatic representation of a device 100 to carry outthe process of the present invention. A control box 150 contains amicroprocessor or other similar control system to control the device inresponse to a vapor temperature sensor 151 a and a liquid temperaturesensor 151 b and a water level sensor 153. The control box 150 controlsa heater (not shown) to raise the temperature of the vessel 101. Thecontrol box 150 also controls a stirring motor 102 and a saltwatersprayer 105 as well as a circulating fan 107. Seawater is stored in asupply container 110 and is sprayed into an evaporation vessel 101 tomaintain the level of fluid therein. Generally, the seawater is heatedprior to being sprayed by heating the entire container 110 or by heatingthe sprayer 105. Waste or solar heat are especially preferred so thatthe system converts waste energy into pure water. The sprayer 105produces a fog-like spray to allow a maximum amount of directevaporation. The total amount of energy required is greatly reduced bythe micro-powder 104, which is located within the vessel 101.

The system functions when the rotating impeller 103 stirs the solutionof micro-powder and warmed seawater. As already explained, themicro-powder tremendously increases the available surface area forvaporization. At the same time interactions of the water molecules withthe particle surfaces reduce water-water interactions to effectivelycause a local reduction in the heat of evaporation of the water. Thiscauses greatly accelerated evaporation of water (arrows). Thetemperature sensors 151 a and 151 b detect the temperature differencebetween the vapor and liquid phases and the vessel 101 can be heated, ifnecessary, (heater not shown) to maintain a temperature differential.The fan 107 circulates the vapor into the condenser 108 where the vaporis converted to liquid water. A check valve (not illustrated) can beprovided so that liquid eater can be drawn off into a water collectionvessel 120 without releasing the pressure differential caused by thecondensation. Additional seawater is sprayed from the sprayer 105 toincrease the water vapor pressure within the vessel 101.

Periodically, the concentrated brine accumulating in the vessel 101 isdrawn off (not illustrated). The micro-powder is recovered byfiltration, centrifugation or simple gravitational settling. In caseswhere a cellulosic micro-powder is used, it is possible to merelydispose of the used powder since it is fully biodegradable. Generally,the concentrated brine may simply be pumped back into the ocean througha dispersal piping system to avoid excessive local increases insalinity. Alternatively, if there is an available market for the brine,it can be used industrially as a chemical feedstock, for example.

In the illustrated device the vessel 101 is 70×80×100 cm in size. Twomotors 102 are set in parallel (only one illustrated) with each motorhaving a capacity of about 1.5 kWh. The micro-powder 104 is stirred bythe impellers 103 at a speed of about 1000 rpm.

The evaporation rate and volume increase with increased rotation andincreased temperature. However, temperatures above an optimal value, maycause decomposition of the powder. In this example, the temperature inthe vaporization vessel is set to no more than 70° C. Inorganicmicro-powders do not decompose at temperatures reached in this device.However, the cellulosic material has superior properties.

The micro-powder stored in vessel 101 can be, for example, a mixture ofwood powder 25 kg and silica 5 kg. The mixture was stirred with theimpeller 103 while thirteen liters of ocean water was sprayed under thecontrolled condition of 70° C. As stirring continued, water was lost byevaporation. Ocean water was added to replace the evaporated water,which equaled about 6 l/hour. If the same experiment were conductedwithout the addition of the micro-powder, less than 1 l/hour would beevaporated. This indicates at least a six-fold improvement due to themicro-powder.

SECOND EXAMPLE

In the second example, contaminated river water was used to emphasizethat invention is not limited to the case of ocean water. Pure water canbe obtained from any aqueous solution contaminated with non-volatileimpurities. For example, irrigation runoff or recycled gray water canreadily be desalinated by the present invention.

The basic system was the same as explained in the first example. Onlythe differences from the first example are detailed. Twenty-five kg ofwood micro-powder was placed in the vessel 101 and agitated by theimpellers 103. Moreover, the control box 150 was set to 50° C. for theevaporation temperature Rather than ocean water impure water taken froma river was fed through the spray nozzle 105 after being pre-heated to40° C. Here 10 l of water was initially fed in slowly to prevent a fallof temperature in the vessel. About 2 l/hr of freshwater was obtainedfrom the condenser 108 as a result. If the same experiment were carriedout without the wood micro-powder, the amount of pure water producedwould be insignificant.

The following claims are thus to be understood to include what isspecifically illustrated and described above, what is conceptuallyequivalent, what can be obviously substituted and also what essentiallyincorporates the essential idea of the invention. Those skilled in theart will appreciate that various adaptations and modifications of thejust described preferred embodiment can be configured without departingfrom the scope of the invention. The illustrated embodiment has been setforth only for the purposes of example and that should not be taken aslimiting the invention. Therefore, it is to be understood that, withinthe scope of the appended claims, the invention may be practiced otherthan as specifically described herein.

1. A method for accelerating the evaporation of water comprising thesteps of: making a mixture of water and a quantity of fine particles,the particles having an average diameter of 100 μm or less, wherein theparticles are metal oxides selected from the group consisting ofalumina, titania, magnesia and iron oxide; agitating the mixture withina container at a temperature below the boiling point of water wherebywater vapor release from the mixture is accelerated.
 2. The method ofclaim 1 further comprising the step of adding energy during the step ofagitating the mixture to maintain a temperature of the mixture.
 3. Themethod of claim 1, wherein the average diameter of the particles is 10μm or less.
 4. The method of claim 3, wherein the average diameter ofthe particles is 1 μm or less.
 5. The method of claim 1, wherein theparticles are hydrophilic.
 6. The method of claim 1 further comprisingthe step of spraying additional water into the mixture to replenishevaporated water.
 7. The method of claim 6, wherein a temperature of theadditional water is adjusted to prevent lowering a temperature of themixture.
 8. The method of claim 1 further comprising the step ofproviding a system to reduce a pressure in the container.
 9. The methodof claim 8, wherein the system of reducing a pressure condenses watervapor.
 10. An apparatus for accelerating evaporation of watercomprising: a container holding a mixture of water and fine particles ata temperature below the boiling point of water, wherein the particleshave an average diameter of 100 μm or less; means for agitating themixture whereby water vapor release from the mixture is accelerated;means for spraying additional water into the mixture to replenishevaporated water; and means for adjusting a temperature of theadditional water to prevent lowering a temperature of the mixture. 11.The apparatus of claim 10 further comprising means for adding energy tothe mixture to maintain a temperature of the mixture while the mixtureis being agitated.
 12. The apparatus of claim 10, wherein the averagediameter of the particles is 10 μm or less.
 13. The apparatus of claim12, wherein the average diameter of the particles is 1 μm or less. 14.The apparatus of claim 10, wherein the particles are composed of amaterial selected from the group consisting of polysaccharidemacromolecules of plant origin, cellulosic macromolecules, proteins,clays, metals, silica and metal oxides.
 15. The apparatus of claim 14,wherein the metal oxides are selected from the group consisting ofalumina, titania, magnesia and iron oxide.
 16. The apparatus of claim10, wherein the particles are hydrophilic.
 17. The apparatus of claim 10further comprising means for reducing a pressure in the container. 18.The apparatus of claim 17, wherein the means for reducing a pressurecondenses water vapor.
 19. A method for accelerating the evaporation ofwater comprising the steps of: making a mixture of water and a quantityof fine particles, the particles having an average diameter of 100 μm orless; agitating the mixture within a container at a temperature belowthe boiling point of water whereby water vapor release from the mixtureis accelerated spraying additional water into the mixture to replenishevaporated water; and adjusting a temperature of the additional water toprevent lowering a temperature of the mixture.
 20. The method of claim19, wherein the particles are composed of a material selected from thegroup consisting of polysaccharide macromolecules of plant origin,cellulosic macromolecules, proteins, clays, metals, silica and metaloxides.